Paul claims that all are under sin (Romans 3:9) and uses a number of biblical quotations to show the unrighteousness and irreverence of man (Romans 3:10a, 18), giving further explanation of his sinfulness and examples of his sin (Romans 3:10b–17). Addressing the Jews in particular (cf. Romans 2:17, “if you call yourself a Jew”), Paul clarifies that they are the audience of the Law and identifies its purpose (Romans 3:19–20).
Romans 3:9–20 concludes Paul’s discussion of man’s unrighteousness in Romans 1:18–3:20.
Paul clearly asserts that both “all, Jews and Greeks [Gentiles], are under sin,” that is, under its power, made obvious man’s many sins (Romans 3:9; cf. 3:13–17). “As it is written” then introduces a number of biblical quotations to show the universal sinfulness of man (Romans 3:10).
Romans 3:10–12 quotes much of Psalm 14:1–3 (almost identical to Psalm 53:1–3). Paul claims as David did that “none is righteous” before God (Romans 3:10; notice Paul’s modification from Psalm 14:1, “There is none who does good”). One could literally translate this phrase, “There is no righteous one,” just as Romans 3:18 could translate, “There is no fear of God.” These two instances of “there is” act as bookends for Romans 3:10–18. Romans 3:19–20 then closes all of Romans 1:18–3:20.
As evidence of man’s unrighteousness claimed in Romans 3:10, the quote from Psalm 14 stack the negatives against mankind—no one understands, seeks for God, or does good but rather turns aside and becomes worthless (Romans 3:10–12; cf. Psalm 14:1–3).